Nonsaturating induction relay

ABSTRACT

210,092. British Thomson-Houston Co., Ltd., (Assignees of Hall, C. I.). Jan. 22, 1923, [Convention date]. Induction relays.-The time-characteristic of an inverse time-limit overload relay of the induction type is improved, so that greater selectivity is obtained for a number of relays in series in the event of a heavy overload, by employing a non- saturated core energized by the supply current and so arranged that an increased leakage flux in relation to the driving flux and varying directly with the current is produced therefrom to cut the disc and produce a retarding torque which increases with the speed of the disc. As shown in Fig. 1, the relay comprises the usual disc 1 on the spindle 2 controlled by the spring 11 actuated by the driving magnet 3 having an energizing coil 25 and shaded poles 3&lt;a&gt;. The poles are longitudinally and rotation ally adjustable on pins at the ends of the magnet; the rotational adjustment may be made, as shown, by a worm-wheel 54 acting through a gear wheel 54&lt;1&gt;. The coil 25 is subdivided into a main single central portion and additional portions which have half their turns on either side of the main portion so as to maintain the central symmetry. The various windings are brought out to a small plug board 41 so that, by means of a plug 61, the central portion alone, or the central portion together with any or all of the additional windings connected in parallel therewith, may be utilized as the energizing winding. By suitable choice of the coils to be energized, the relay may be adapted to circuits of different normal amperage. The disc is held in its normal position, against the action of the spring 11, by a pin 9 on the gear-wheel 7 abutting against the back-stop 10. This stop is adjustable over the scale 13 and its position determines the necessary travel of the disc before the stop presses together contacts 14, 15, which are electromagnetically maintained, and close the tripping circuit. Serrations of progressively increasing depth are formed in the disc to give gradually increasing torque, thereby compensating for the increasing control torque of the spring 11. The serrations cease at the correct point to supply the final increased torque for the switching movement. The driving magnet lies over a chord of the disc and a leakage flux, producing a retarding torque proportional to the square of the current and to the speed of the disc, always cuts the disc. Due to this leakage flux, the increase in the time of action of the relay is made greater for large overloads and smaller for small overloads than can be obtained with the retardation due to the usual permanent magnets 4, 5 alone.

Flled Jan 22. 1923 2 Sheets-Sheet 1 C I HALL NONSATURATING INDUCTIONRELAY May 26, 1925..

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c. l. HALL NONSATURATING INDUCTION RELAY Filed Jan. 22, 3 2 Sheets-Sheet2 Current pick-up paint A Invert/or Chester- I- H Mf% His Attorney.

Patented May 26, 1925.

UNITED STATES CHESTER I. HALL,

PATENT OFFICE.

OF FORT WAYNE, INDIANA, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, ACORPORATION OF NEW YORK.

NoNsA'rURATING nmucrron RELAY.

Application filed January 22, 1923. Serial No. 614,331.

these improvements as embodied in an inverse time limit overload relayof the induction type which employs a shaded pole electromagnet forrotating a disk of conducting material.

One of the objects of my invention is to so design or adjust devices inwhich a plate is electromagnetically moved, particularly inverse timelimit devices, asv to impart thereto a desired characteristic. Forexample, I may by means of this invention impart a desired form andposition to the time-current curve of an inverse time limit overloadrelay in the manufacture of the device, or in the course of the usethereof.

Another object isto improve the action of such devices and particularlyto compensate in a new manner, for a varying torque exerted ontherotating disk such as the varying counter torque exerted when the diskin turning winds up a spring.-

A still further object is to simplify and cheapen the construction,particularly by dispensing with magnetic saturation and features whichhave been commonly employed to secure a usable characteristic or curveby means of magnetic saturation.

Another object is to secure adaptability of the same device to currentsof diiferent orders of magnitude.

Other objects will be apparent from the following detailed descriptionand explanation.

In the accompanying drawing the im-;

provements which constitute my invention are shown embodied in aninverse time limit overload relay of the induction type employinga'shaded pole ma net to rotate a disk of conducting materiawell-understood in the art are used to pro- Such. relays as is tectelectrical lines and apparatus against injury by the persistence for toogreat a time of an excessive current. A current greater than the line orapparatus is designed to bear is called an overload. A small overloadmay persist for a relatively long time before any damage is, done. Alarge overload is harmful if allowed to persist for a relatively shorttime. Inverse time limit overload relays are intended to actuate a cir-.

cuit breaker or otherwise remove the overload only after theoverload haspersisted for a length of time which is longer or shorter as theoverload is smaller or' larger. Such devices while affording protectionfrom damageby overloads, do not interrupt the circuit when the overloadis one which would not persist long enough to be harmful even ifprotecting devices were not used.

An example of such an inverse time limit overload relay used in the pastis found in the patent to, Ricketts, No. 1,286,415. That device like therelay shown in this applica tion has a shaded pole electromagnet whichrotates a copperdisk against the torque of a coiled spring, and againstthe drag of a permanent magnet, to close a local circuit and actuate acircuit breaker. But Rickettss device depends upon the magneticsaturation of iron to obtain the proper time of action for certainoverloads. This requires special additional parts. My device does notdepend upon or employ magnetic saturation of iron. In my device theproper time of action for both small and large overloads is securedentirely by other means. 7 1

Inverse time limit overload rela s have also been suggested heretoforewhich em-' ploy a shaded pole electromagnet acting on a copper diskagainst an initial torque and f 884,066 to Brown discloses a relay inwhich a shaded pole electromagnet rotates a copper disk against a torqueproduced by a weight and against the drag of a permanent magnet, andwhich does not appear to involve devices so far as I am aware have nevercome-into use. The reason'for this, I believe, is that ithas beenimpossible to designthem so that the time of action for both themagnetic saturation of iron. But suchf moderate and larger overloadswill meet the I make them desirable.

requirements of practice. 'In other words,

the time-current curve of such devices did not conform closely enoughwith the timecurrent curve of injury through overload to This difficultyis overcome by my invention herein disclosed.

In the drawings accompanying and forming part of this application: 7

Fig. 1 is a perspective view of the essential features of an inversetime limit overload relay embodying my invention.

Fig. 2 is a diagram of the windings and connections of the electromagnetwhich cooperates with the conductive disk.

Fig. 3 is a diagram showing the circuits and connections for operating acircuit breaker and showing also the circuit connections between therelay and the line.

Fig. 4 is a set of curves to illustrate the principle of the invention.

Fig. 5 is a detail view of that end of the electromagnet whichcooperates with the conducting disk, showing an adjustable constructionof shaded pole pieces.

In the drawings, the reference character 1 designates a disk ofconducting material mounted on a rotatable shaft 2. An electromagnet 3and permanent magnets 4 and 5 are mounted so as to pass magnetic fluxthrough the disk 1. The pinion 6.on the shaft 2 engages the gear 7 whichis mounted on the rotatable shaft 8. A pin 9 mounted on the gear 7 is.normally held against a back stop 10 through the action of the spring 11on the shaft 2. The position of the back-stop 10 is adjustable by meansof a lever 11 having a pointer 12 traveling on a scale 13.

The coil 25 is energized directly or indirectly by the current in theline which is to be protected. In Fig. 3 there is shown for this purposea transformer circuit 24 having in series therewith the secondary of atransformer 23 and the coil 25. The primary of this transformer is inthe line 20 which is to be protected. The transformer should not be asaturating transformer; the currents generated in the secondary thereofmay be, and preferably will be, strictly proportional to the currents inthe line 20 for all loads or overloads so far as the proper operation ofthe relay herein disclosed is concerned.

Whenam overload occurs the torque produced by the shaded poles 3, 3tending to rotate the disk overcomes the counter torque of the spring 11and the disk rotates against the counter torque of the spring 11, andagainst the drag of the permanent magnets 4 and 5 and against the dragof the driving magnet 3. If the overload is small the speed of the disk1, which may be' regarded as constant for any given overload, will berelatively slow. If the overload is large, the speed of the disk 1 willbe relatively fast.

If the overload persists until the pin 9 accircuit 20. When the maincircuit 20 has been broken the coil 25 of the driving magnet 3 isdeenergized and the disk 1, gear 7 and pin 9 are returned to theirinitial positions by the spring 11. The operation of the circuit breakeralso breaks the local circuit 17 at '22 allowing the movable contact 14to return to its normal position. When the circuit breaker 19 is resetto close the main circuit 20, the break in the local circuit at 22 isclosed so that the local circuit is then ready to respond to theoperation of the relay upon the next occurrence of an overload.

The coil 25 of the driving magnet 3 is preferably divided into sectionswhich are provided with connections and taps as clearly indicated on thediagram, Fig. 2. In this diagram, 26 represents a central coil one endof which connects at 23 with one end of the transformer circuit 24. itsother end is connected to the tap wire 27 and to one end of the splitcoil 28, 28. The other end of the coil 28, 28 is connected to the tapwire 29 and to one end of the split coil 30, 30". The other end of thecoil 30, 30 is connected to the tap wire 31 and to one end of the splitcoil 32, 32. In like manner the connections are extended through tapwire 33, the split coil 34, 34, and tap wire 35. The tap wires 27, 29,31, 33 and 35 are connected respectively to conducting bushings 36, 37,38, 39 and 40. These bushings are spaced from the conducting tap plates41 which is provided with openings 42, 43, 44, 45 and 46 registeringwith the opening in the bushing so that by means of a removableconducting pin 61 any desired tap may be electrically connected to theconducting tap plate 41. The plate 41 is connected by the wire 47 to thetrans former circuit 24 at 48.

The coil 25 is thus subdivided so as to adapt the same device for usewith circuits of different normal amperages. For example, the devicemight be designed so as to operate properly in connection with a circuitwhich normally carries 6 amperes when the pin 61 is inserted in thebushing 36 and only the central coil 26 is in the circuit 24, and sodesigned as to act properly with a 5 ampere circuit when the pin 61 isin bushing 37 and the coils 28 and 28 are functioning in additional tothe coil 26. The purpose of splitting each additional coil into twosections mounted respectively on the different sides of the coil 26 isto maintain the distance of the middle point of the effective portion ofthe coil from the pole 3 unchanged by the inclusion or exclusion of thevarious split coils in the eneris hereinafter madeapparent.

The pole pieces 3 and 3 of the driving magnet 3 are preferably made"adjustable both axially and circumferentially of their axes. Thisconstruction is clearly shown in Fig. 5 where 3 and 3 are the polepieces provided with the shading coils 50 and50 and held in position bymeans of the axially extending screws 51 and 51 passing through the endsof the legs of the driving magnet 3. The poles are held in desiredvertical and circumferential adjustment by the set screws 52, 52", and53. A screw 54, Fig. 1 cooperating with a gear 54' on the pole piece maybe provided to facilitate the circumferential adjustment of the polepiece. While this adjusting screw and gear are shown only on the lowerpole piece the upper pole piece might of course be similarly provided.While both pole pieces are shown ad-' justable, the adjustments ofcourse could be provided on one only. The purpose of the circumferentialadjustment of the shadedpoles is to vary the torque which they producetending to'turn the disk 1. The force which they exert tending to turnthe disk may be varied from zero to a maximum by changing the directionof their pull from, a

direction radially of the disk 1 to a direc tion circumferentiallythereof.

The disk 1 is provided with a series of serrations or notches of varyingdepth in its circumference. Such serrations adjacent the shaded polesincrease the resistance to the eddy currents generated by the shadedpoles in the disk and thus lessen the pull tending to turn the disk; thedeeper the serrations, the less the ull. By having the serrationsdeepest a -'tion remains constant. The purpose of this is to offset theincreasing counter torque exerted by the spring 11 as the rotationof-the The depth of the serraaccordance with the variation in the of thespring 11. v I

At the point on the circumference of the disk 1 which is adjacent theshaded poles when thedisk is, nearly at the end of its journey and aboutto press the contact 14 pull against the contact 15 the serrationssudden- 1y terminate. This gives a sudden increase in the next torqueturnin the diskand causes contacts 14 to be cosed on contact that partof the clrcumference of the disk which is adja thescale 12, the distancethrough which the I disk 1 must move in order to actuate the contacts 14can be varied and the time of operation correspondin ly varied. Thisdevice is particularly use 'ul in my relay where it is desired to insurethat a number of relays on the .same line shall operate in a certainorder. 1

I have discovered that if a disk relay operated by an alternatingelectromagnetic flux is so constructed that a substantial leakage of theelectromagnetic flux of the driving magnet cuts the disk, an increase inthe time of action is secured which is large for large overloadsandsmall for small overloads, as compared with the increase in the time ofaction which may be secured by increasing the strength of the permanentmagnet. This difference in the action of the permanent magnetic flux andthe electromagnetic leakage flux is due to thefollowing facts. Theretarding torque of the permanent magnet varies with the speed of thedisk but is independent of the strength of the current which actuatesthe relay. The electromagnetic flux cutting the disk, both polar andkeep down the speed of the. disk, other things being maintained thesame, is to increase the time of action of the relay for large overloadsand to decrease it for small overloads. In other words, the time-currentcurye is lifted and made flatter for large overloads and is lowered forsmall overloads and is given a sharper curvature be tween certainmoderate overload values.

Another striking result of employing a leakage of the electromagneticflux to retard the motion of the disk is that the time can be made toapproach any definite value as desired, within reasonable limits, whenthe magnitude of the current is increased without limit. Expressed inthe terms of mathematics, the greater the effective strength of theelectromagnetic leakage flux when the current value is increased withoutlimit. In other words, when different strengths of a permanent magnetare solely rehed upon to secure different curves, all

the curves will have the same asymptote at their high current ends andthe value of the time of action of the relay for infinite current willbe the same for all strengths of the permanent magnet.

The curves in Fig. 4 though not made from any particular tests and notto scale illustrate the effects which pertain to the use of a leakage ofthe flux of the driving magnet cutting the diskto oppose the motion ofthe disk. Dotted curves A and B may be taken to represent thetime-current characteristics of two relays in which there is nosubstantial amount of electromagnetic leakage cutting the disk, curve Abeing secured by using a weak permanent magnet and curve B by using astrong permanent magnet. Solid curves C, D and E will then representtime-current characteristics which can be secured by employing adisk-cutting leakage of the electromagnetic flux of the driving magnet.Curve C is such a curve as could be obtained by means of a certainamount of such a flux in a relay which has the same weak permanentmagnet as the relay of curve A. It will be noted that the time of actionat the high overload end of the curves is as great in curve C as incurve B but that for moderate overloads the time of action is much lessin curve C than in curve B. Curve D is such a curve as could be obtainedby using a disk-cutting electromagnetic leakage fiux in a relay whichhas the same strong permanent magnet as the relay of curve B. It will benoted that the time of action at high overload is much larger on curve Dthan on curve B, but that for moderate overloads there is no suchdifference between the curves D and B as there is between curves B andA. An indefinite number of different curves can be secured lying betweenthe curves A and D by varying the disk-cutting electromagnetic leakageflux and the strength of the permanent magnet between the values whichgave curves A and D.- Curve E is an example of such a curve.

The general principles for thus controlling the shape and position ofthe curve are (1) that a change in the disk-cutting electromagneticleakage flux effects a substantial change in the time of action even forthe most excessive overloads, (2) that any change in the disk-cuttingelectromagnetic leakage flux effects approximately the same change inthe time of action for moderate overloads as for large overloads, (3)that changes in the effective strength of the permanent magnet are ofpractically no effect on the time of action for extremely largeoverloads, and (4) that changes in the effective strength of thepermanent magnet cause much larger changes in the time of action formoderate overloads than for large overloads.

In general, the curves characterizing relays in which the time of actionis more or less dependent on a leakage of electromagnetic flux cuttingthe disk, conform more closely to the time-current curves of injury byoverload than do the curves of relays in which the permanent magnet isprincipally depended upon. And by varying the amount of theelectromagnetic leakage flux cutting the disk and the effective strengthof the permanent magnet, the shape of the curve can be controlled andgiven a wide variety of forms to suit special conditions to an extentthat so far as I know was not before possible in relays which did notemploy magnetic saturation. This proper shaping-of the characteristiccurve is very important where several relays are to be used upon thesame line or network for the purpose of segregrating that section of thesystem in which an overload originates without interfering with theservice throughout the rest of the system.

In order to cause the disk 1 to be cut by a substantial leakage of theelectromagnetic flux from the magnet 3, the legs of this magnet may beextended across a chord of the disk as shown in Fig. 1. The amount ofthe leakage flux may be controlled by placing the center point of thecoil 25 nearer or farther from the pole 3. The more remote the coil isfrom the pole, the greater the leakage. The leakage may also becontrolled by varying the cross-section of the iron core of the coil 25;the smaller the cross-section of this core, the greater the leakage.This does not mean that the core becomes saturated, or approximatessaturation. The amount of leakage increases upon a decrease in thecross-section of the core for all substantial flux values while thevariation of the flux is in proportion to the variation of the currentin the energizing coil. The amount of the electromagnetic flux cuttingthe disk can also be varied, of course, by changing theextent to whichthe legs of the electromagnet project over the disk. Moreover anychanges in the Hill distance from the center of the disk to the point ofapplication of disk-cutting electromagnetic leakage flux has the sameeffect as a change in the amount of the flux. An increase. in thedistance from the center serves the same purpose as an increase in theamount of this flux.

While I now regard "the use of a leakage of the electromagnetic fiuxcutting the disk,

either alone or in connection with a permanent magnet, as the best meansof obtaining a proper form for the time current curve, a like control ofthe shape of this curve to that which has been hereinaboveexplainedcanbesecured by adjusting the shaded poles 3, 3", about theiraxes, so as to reduce the pull which they exert circumferentially on thedisk 1 without reducing the drag of the electromagneticflux upon thedisk. A like control can also be had b varying the resistance of theshading coi or otherwise lessening its effectiveness. Each of thesechanges has the same effect upon thev characteristic curve as theprovision of a leakage of electromagnetic flux cutting the disk.

In fact a like control may be had by any means which substantiallyincreases the ratio of the torque of the electromagnetic drag at uni-tangular velocity of the disk, to the electromagnetic torque whichmaintains the disk at that velocity, over the value of this ratio whenthe electromagnetic flux which is producing drag is also fully effectivein producing disk-advancing torque.

This may be more simply stated by theadoption of a convention. In therotation of conducting disks by shaded pole magnets in the prior art thesole purpose desired of the shaded pole magnet was in general to rotatethe disk. The forward torque of the electromagnet was all that was wantethereof. The electromagnetic flux cutting the moving disk necessarilyproduced a counter torque but this was .not 'wanted. The electromagnetswere therefore in genferal so designed as to get the maximum forwardtorque. .The electromagnetic flux passing through the disk wasconcentratedas much as possible and applied asfaras possible from thecenter of the disk.. Leakage flux was not passed through the disk. Theshaded pole was designed for maximum efiiciency in the production offorward torque and so placed that its pull was directly circumferentialof the disk and as far from the center as practicable. Though theapplication of the disk-cutting flux at the outer edge of the disk alsocaused this disk-cutting flux to exert as much counter torque as thatamount of disk-cutting flux was capable of. exerting. Fig. 1 of thepatent to Brown to which attention has of such a shaded pole magnetdesigned to fully develop its possibilities for producing forward torqueand incidentally developing as much counter torque as the amount .offlux which it passes through the disk is capable of developing. Let usregard such a device as fully developing both the forward and countertorque capability of that particular amount ofelectromagnetic flux whichit causes to cut the disk at any time.

Now if the design is such that the forward torque capability of thetotal electromagnetic fiux cutting the disk is not fully developed andthe counter torque capability is fully developed the special timecurrent characteristics hereinaboyedescribed are secured. An example ofthis is where 1 part of the cutting flux is a leakage flux which is sofar from the shading coil that it is not fully effective in theproduction of forwardtorque. This result will be secured likewise ifneither the forward torque capability nor the counter torque capabilityof the cutting flux is fully developed but the counter torque capabilityis more fully developed than the forward torque capability. An exbesecured if some means were devised forincreasing the counter torque ofthe cutting electromagnetic flux beyond the value which it has in suchdevices as Fig. 1 of the Brown patent, without also corres ondingly in-.

creasing the forward torque 0 this flux. In

general, this result is secured whenever the counter torque capabilityof the total electromagnetic flux cuttin the disk is more fullydeveloped than t e forward torque d capability thereof, the fulldevelopment of these torques of which this flux is capablebeingunderstood to mean that development found in such a device as that ofFig. 1 of Brown Patent, No. 884,066 as has been hereinabove explained.

To get a. very high value of the ratio of counter torque to forwardtorque, two or more of the means hereinabove referred to for thispurpose or other means may be adopted in the same device. For instance,the legs of the electroma et may be placed along a chord of the dis thecross section of the core made small, and the coil located well backfrom thepole, all to secure a large leakage flux cutting the disk andthereby counter torque wasnot desired, the compact develop a largecounter torque without correspondingly developing theforward torquecapability of the cutting flux, and in addithat its pull is largelyradial, all of which lessen the forward torque without reducing thecounter torque.

If in the course of the design of a relay a change is made in the ratioof the electromagnetic counter torque to the electromagnetic forwardtorque, by changing only the amount of the electromagnetic drag or thedistance of its point of application from the center of the disk, theeffect of the per manent magnet upon the characteristic curve of therelay is not substantially changed. But if the change in-the ratio ofthe torque of the electromagnet drag to the motion producing torque ismade by changing the motion producing torque, the effect of thepermanent magnet upon the characteristic'curve is altered. A decrease inthe motion producing torque with the attendant decrease in the strengthof the spring 11 necessary to maintain the pick-up point at the samecurrent value, will increase the efi'ect of the permanent magnet so thatif it is desired to leave the effect of the permanent magnet unchanged aweaker permanent magnet must be used or its efl'ectiveness otherwisediminished.

The improvements hereinabove set forth specifically in connection withan inverse time-limit relay may obviously be applied to the control ofthe speed of rotation of the disk in devices other than relays. And theinvention in its broadest aspect is not limited, to disks or to rotatingmembers but may be applied to movable members which move in straightlines or on arcs of curves. Therefore while I have shown and describedthe various features of my invention embodied in one specific form ofelectrical instrument, I do not wish to be restricted in the protectionof my invention except as required by the prior art and by thelimitations of the claims,

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. An electrical device comprising a movable member of conductingmaterial, a non-saturating electromagnetic means which sends alternatingelectromagnetic flux through the movable member, said electromagneticmeans having -a pole with a shading coil thereon, the flux through theshad 1 p0 e constituting the main cause of the advance of the movablemember, and means whereby a portion of the electromagnetic flux sentthrough-the movable member by the electromagnetic means does not passthrough the shaded pole and is of relatively little effect in causlngthe advance of the 60 movable member.

2. An electrical device having in combination a rotatable disk ofconducting material, a non-saturating electromagnetic means comprising ashaded pole electromagnet which sends an alternating electromagneticflux through said disk, the flux through the shaded pole or polesconstituting the main cause of the advance of the disk, saidelectromagnet extending across the disk so that a substantial leakageflux cuts the disk, said leakage flux being of relatively little effectin causing the advance of the disk, and means additional to theelectromagnetic fluxes for opposing the advance of the disk.

3. An inverse time limit device having in combination a movable memberof conducting material, non-saturating means comprising a shaded poleelectromagnet for advancing said movable member, said electromagnetextending across the movable member so that a substantial leakage fluxcuts the movable member.

4. An inverse time limit device having in combination a rotatable diskof conducting material, non-saturating means comprising a shaded poleelectromagnet for efi'ecting forward rotation of the disk, saidelectromagnet extending across the disk so that a substantial leakageflux cuts the disk, the energizing coil of said electromagnet beingspaced from the adjacent pole so as to promote leakage cutting the diskand means additional to the electromagnetic fluxes for opposing theforward motion of the disk.

5. An inverse time limit overload relay comprising in combination arotatable conducting disk, non-saturating electromagnetic meanscomprising an electromagnet which has a shaded pole for rotating thedisk, said electromagnet extending across the disk so that a substantialleakage flux cuts the disk, the energizing coil of said electromagnetbeing spaced from the adjacent pole so as to promote leakage cutting thedisk, a permanent magnet also cooperatin with said disk and meansbiasing the dis to initial position.

6. An inverse time limit device having in combination a rotatable diskof conducting material, an alternating current electromagnet embracingthe disk with its poles near one edge of the disk and its legs extendingacross the disk, an energizing coil therefor, one of the poles beingrotatable about an axis perpendicular to the plane of the disk,shadlngcoils on the poles, a ermanent magnet also embracing the isk,means for holding the disk at rest when the current in the energizingcoil is below a predetermined value, the energizing coil being spacedfrom the adjacent pole or poles so as to cause a leakage ofelectromagnetic flux which cuts the disk but does not pass through thepoles.

7 An electrical device having a movable member whose speed changes withchanges in an actuating current, a shaded pole electromagnet for sendingan alternating magnetic flux therethrough which causes the lit) forwardmotion thereof and also produces a retarding pull thereon, the fluxthrough the shaded pole constituting the 'main cause of the advance ofthe movable member, the

shading coil being such that its tendency tomove themovable member isless-than that which could be produced by a shading coil withthe sameamount of alternating magnetic flux passing'through the shaded pole andmovable member, and means additional ed to send an alternating magneticflux 4 through said disk which causes the rotation thereof and alsoproduces a retardingdrag thereon, the position of the shading coil beingsuch as to diminish the torque thereof tending to rotate the diskwithout correspondingly reducing the counter torque of theelectromagnetic flux upon the disk.

9. An inverse time limit device having in combination a rotatable diskof conduct- I ing material, a shaded pole electromagnet adapted to sendan alternating magnetic flux through said disk which causes the rotationthe movable member and give the same its forward motion, means foradjusting the strength of the pull of the electromagnetic means whichgives the movable memberv its forward motion without substantiallyvarying the drag which the electromagnetic means exerts on the movablemember when the latter is in motion at a given speed and meansadditional to the electromagnetic fluxes for opposing the forward motionof the movable member.

11. An inverse time limit device having in combination a rotatableconducting disk, a shaded pole electromagnet sending an alternatingmagnetic flux through said disk to rotate it, a pole of the magnet witha shading coil thereon being adjustable about an axis perpendicular tothe disk.

'12. An electrical device comprising a movable member of conductingmaterial whose speed changes with changes in an actuating current,non-saturating means for passing a varying magnetic flux therethrough toproduce an advancing tendency which varies with the strength of thevarying magnetic flux passing throughthe movable member and causes itsforward motion, and a retarding tendency which varies with the strengthof said magnetic flux and with the speed of the movable member, thecapability of the varying magnetic flux which passes through the movablemember for producing the retarding tendency being more fully developedthan its capability for producing the advancing tendency.

* 13. A rotatable disk of conducting material, a non-saturatingelectromagnetic means comprising a shaded pole electromagnet for passinga magnetic flux through said disk to produce the forward torque whichcauses the same to move and a retarding efl'ect thereon which .isproportional to its speed, the capability of the electromagnetic fluxpassing through the disk for producing counter torque being more fullydeveloped than its capability for producing forward torque and meansadditional to the electromagnetic flux for opposing the for- Ward motionof the disk.

14.. An inverse time limit device having in combination a rotatableconducting disk, af non-saturating electromagnetic means comprising ashaded pole electromagnet for sendin an alternating magnetic fluxthrough said disk which produces thereon the forward torque which givesthe disk its motion and also a counter torque thereon which isproportional to the speed of the disk, the capability of the alternatingma netic flux passing through the disk for producin counter torque beingmore fully develop than its capability for producing forward torque, apermanent magnet also sending flux through said disk and means biasingsaid disk to its initial position.

15. A time limit overload device having in combination a movable memberof conducting material and a non-saturating electromagnetic meanssending an alternating magnetic flux through the movable member toproduce a pulling action on the movable member to move it and aretardinlg action which varies with the velocity thereof, the retardingaction of the alternating magnetic flux sent through the movable member,being proportioned to the pulling action thereof to obtain a relationbetween the speed of the movable member and the size of the overloadwhich conforms to the relation between the period of safe duration ofthe overload and the size of the overload.

16. A time limit overload device having in combination a rotatableconduct-ing disk which operates protective apparatus upon movementthrough a predetermined are, a non-saturating electromagnetic meanscomprising a. shaded pole electromagnet for sending an alternatingmagnetic flux through the disk to produce the forward movable member andalso produces a drag speed of the disk, a permanent magnet also sendingmagnetic flux through the disk, and means biasing the disk to itsinitial position, the counter torque of the electromagnetic means andthe drag of the pennanent magnet being proportioned to the forwardtorque of the electromagnet to obtain a relation between the time ofaction of the relay and the size of the overload which conforms to therelation between the period of safe duration of overload and the size ofthe overload.

1 7. A movable member of conducting material, an electromagnet whichoperates the thereon which is proportional to the speed of the movablemember, a leg of the electromagnet extending over the movable member, anexciting coil on said leg, said coil being subdivided into a centralcoil and pairs of coils, one coil of each pair being on one side of saidcentral coil and the other coil of each pair being on the other side ofsaid central coil.

18. An inverse time limit device comprising a movable member ofconducting material, a shaded pole electromagnet which sends analternating magnetic flux through the movable member to cause itsmot-ion and also exert an opposition to the motion of the movable memberwhich is proportional to the speed of the movable member, a leg of theelectromagnet extending over said movable member, an exciting coil, saidcoil been subdivided into a central coil and pairs of coils, one coil ofeach pair being on one side of said central coil and the other coil ofeach pair being on the other side of said central coil, and taps thesecoils and connections so that current may be sent at will through thecentral coil or through the central coil and any desired number of thecoils on each side thereof.

In witness whereof, I have hereunto set my hand this 20th day ofJanuary, 1923.

' CHESTER I. HALL.

